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Iowa gets second bioreactor

By Staff | Jun 19, 2009

Keegan Kult, watershed management specialist, explained how the bioreactor was built and how it will work to reduce nitrates in tiled runoff water.

WEBSTER CITY – Iowa’s second wood chip biofilter, also known as a bioreactor, was installed Thursday on the Hamilton County farm of Arlo Van Diest, a few miles west of Webster City.

The bioreactor is a project designed to remove nitrates from field runoff before the water flows into the nearby Boone River. The state’s first bioreactor was installed in Greene County last September. On Thursday, a field day was held for about two dozen onlookers, most of them media representatives, to witness the installation of Iowa’s second of several planned bioreactors.

According to the Iowa Soybean Association’s environmental program, since much of the land in north central Iowa is artificially drained by tiling, there has developed a growing problem of high concentrations of soluble nutrients reaching Iowa’s streams and rivers,

This can be harmful for the watersheds’ ecosystems.

The ISA’s environmental program noted that edge-of-field treatment systems, such as buffer strips, have been employed over the past few decades to reduce nitrate-ladened runoff into Iowa’s watersheds. But as research is showing, the ISA claims, aside from large rain events, most water leaving agricultural fields is through subsurface tile flow bypassing contact with surface filter systems.

Woodchips are dumped into the bioreactor where they will be used as a carbon source through which tile water can flow and microorganisms will break down any nitrates present and release the gas byproduct into the atmosphere.

But this is changing as the Agriculture’s Clean Water Alliance, in partnership with the Iowa Soybean Association, both based in Urbandale, and the Sand County Foundation, based in Monona, Wis., teamed up to install bioreactors through out the Des Moines River and Raccoon River watersheds.

Joe Britt, of the Sand County Foundation, said there’s “lots people can do to keep things from the fields out of the watershed. Caring for land should also mean caring for our water.

“Land does well by the farmer. A farmer does well by the land (and) that should mean as much about the water,” Britt said.

ACWA President Dave Coppess said the installation of the bioreactor is just one step in many of the projects that will be done in solving water quality issues.

“The efforts going on here are just the beginning. We’re taking little steps forward and our future generations will enjoy the efforts done today,” Coppess said.

According to the ACWA, a bioreactor is designed to remove nitrates from field runoff flowing through tile lines. These systems, ACWA claims, are easy to construct, relatively inexpensive and, unlike above-ground systems that capture surface water, they take little or no land out of production.

A bioreactor is a wide underground trench that is filled with a carbon source, in Iowa’s case, usually wood chips. Keegan Kult, ISA watershed management specialist, said the trench will feature wood chips layered 3 1/2 feet in depth, covered by a geo-fabric, which will help water flow and keep the 18 inches of top-soil that will cover the trench from shifting.

Water flowing down the tile line from the field is redirected into the wood chips. Micro-organisms colonize the wood chips and use them as a food source, while breaking down the nitrogen in the water and expelling the byproduct as gas into the air. And since the nitrogen is released as a gas, a bioreactor functions without becoming a sink for nitrogen.

The bioreactor located on Van Diest’s farm, was built on a buffer strip near the edge of his field. Kult said it is fed by a tile line that drains 40 acres, plus additional water coming from an older clay tile line.

An upper and lower control structure, provided by Agri-Drain, of Adair, are installed in the bioreactor that diverts the water through the bioreactor, while monitoring the depth of the water entering and leaving the structure.

Todd Sutphin, state watershed coordinator for the ISA, said the way the bioreactor works is easy to understand.

“It’s pretty basic, we’re just using microbes to treat water,” said Sutphin.

In addition to the bioreactors that have been placed in Greene and Hamilton counties, Sutphin said there are plans for at least four more to be installed, with the next one slated for early next month near Corwith in Hancock County.

Contact Kriss Nelson by e-mail at jknelson@frontiernet.net.

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